Renal phosphate clearance in the fetus

Abstract Basal renal Pi excretion in the fetus is very low compared to that in older children and in adults. Studies have demonstrated that the fetal kidney responds to stimuli known to effect renal tubule Pi reabsorption in the adult, and thus, developmental immaturity is not a factor in renal Pi handling in early life. Preliminary studies in fetal lambs showed increased tubule Pi reabsorption following increased filtered Pi load, and Trn phos was not demonstrated. In these studies, the low GFR in the fetus limited filtered Pi load to less than that in children and adults, and is, therefore, a major factor effecting renal Pi handling during early development. In adults, Serum [Pi] is regulated by Tm phos /GFR, and similar studies in infants have not been published. Corvilain and Abramow showed higher Tmphos and Tm phos /GFR, in children age 5–15 yr compared to values for adults. We have formulated the hypothesis that low urinary Pi excretion in early life results primarily from low GFR, and secondarily from elevated Tmphos, which may be mediated in part by growth hormone. Since studies of Tm phos /GFR, in the fetus and in infants have not been published, the role of the kidney in regulation of serum [Pi] in early life remains unclear.